Embodiments of the present invention relate generally to electrochemical devices, and particularly, to liquid-free lithium-air cells incorporating solid electrolytes comprised of glass-ceramic and/or polymer-ceramic materials having enhanced ionic transport and catalytic activity.
In electrochemical devices such as batteries, fuel cells, and sensors, oxidation and reduction of chemical species such as hydrogen and lithium is carried out at an anode. The ionic species travel through the cell internally, i.e., from the anode through an ionic conductor or electrolyte, to a cathode. The electrolyte may be in liquid or solid form. Lithium ion batteries currently in use typically comprise a carbon anode, a porous polymer membrane containing a liquid electrolyte comprised of, for example, lithium salts dissolved in organic solvents, and a cathode comprising a transition metal oxide.
Liquid electrolytes have typically been preferred in commercial electrochemical devices such as lithium ion batteries because they exhibit high conductivity (about 10−3 to 10−1 Scm−1). However, a high temperature environment can lead to rupture, ignition, and even explosion of liquid electrolyte-based lithium batteries due to reactions involving the liquid electrolytes, polymer membrane and the transition metal oxide cathodes. Therefore, it has become desirable to develop more thermally stable and safe lithium batteries with high energy and power densities.
While it is possible to use solid electrolytes in lithium batteries, solid electrolytes are generally associated with lower conductivity and therefore have typically been of lesser interest for commercial applications. There are a number of different approaches which have been employed to enhance the conductivity of solid electrolytes. In recent years, higher conductivity solid electrolytes have been developed using materials such as Li1+xAlxTi2−x(PO4)3 and Lix+1GexTi2−x(PO4)3. These ionic conductors have shown conductivity of about 10−3 Scm−1 near room temperature; however, they are still typically not as conductive as liquid electrolytes.
As an alternative to lithium ion batteries, interest has increased in recent years in the development of lithium-air batteries. Such batteries comprise a lithium anode coupled to atmospheric oxygen through an air cathode such that the reduction of oxygen forms lithium peroxide. The cathode reactant (oxygen) is virtually an unlimited source in atmospheric air. Therefore, the air does not need to be carried in the battery. The primary reason for interest in developing lithium-oxygen batteries is the large theoretical energy density possible compared with state-of-the-art lithium batteries. For example, the energy density of a lithium air battery is about 3000 Wh/kg, which is about an order of magnitude greater than lithium ion batteries. In addition to the abundant air supply, the lithium air battery is also environmentally friendly and provides improved safety over the use of lithium ion batteries. However, the development of lithium-air battery cells has been hindered by the lack of suitable membranes which can contain lithium metal and safely carry out electrochemical reactions, and the limited rechargeability of the battery due to the limited cycle life of the lithium anode.
Accordingly, there remains a need in the art for a lithium-air battery utilizing an electrolyte membrane which provides efficient ionic transport, and which exhibits high conductivity and rechargeability.